In recent years, with a great amount of FTTH (Fiber To The Home) and 3G/4G network construction in China, demands for optical devices become greater, and a system vendor's requirements for optical devices also become higher. As a result, development of optical devices featuring a high rate, long-distance transmission, miniaturization and low power consumption has become a focus that attracts attention of equipment vendors and device vendors.
With miniaturization development of a laser transmitter, packaging manner thereof has changed from conventional Butterfly packaging to XMD (10 Gbit/s Miniature Device) packaging. When the number of demanded pins is large, if the pins are all disposed at a same side surface of a ceramic substrate, volume of the ceramic substrate needed for use is accordingly increased, so that the laser transmitter occupies a greater space, which goes against miniaturization development of a laser transmitter. Therefore, in the existing technology, pins are welded to opposite surfaces of a same ceramic substrate, so as to reduce volume of the ceramic substrate. As shown in FIG. 1, provided is a schematic diagram of an existing laser transmitter adopting XMD packaging, which includes an optical fiber adapter 01, a cavity 02 and pins 03. Electrical components of the laser transmitter include a laser inside the cavity 02 and another electrical component (not shown in the figure). Light emitted by the laser enters an optical fiber through the optical fiber adaptor 01. The pins 03 are welded to opposite surfaces of a same ceramic substrate (not shown in the figure) in the cavity 02, and are connected to an external circuit for supplying power to the laser and the another electrical component.
FIG. 2 is a schematic diagram of an internal structure of the laser cavity 02 shown in FIG. 1. FIG. 3 is a schematic diagram of a ceramic substrate in FIG. 2. The cavity 02 includes a heat sink 04, a laser 05 and a first ceramic substrate 06. A conductive layer is adhered to a surface of the heat sink 04, and a cathode of the laser 05 is laminated on the conductive layer. The laser 05 has an anode welding spot 051 on an upper surface thereof. The first ceramic substrate 06 includes a conductive path 0A on an upper surface thereof, and a conductive path 0B on a lower surface thereof. The conductive paths 0A and 0B are respectively welded to pins 03 located on opposite surfaces of the first ceramic substrate 06. The anode welding spot 051 is connected to the conductive path 0A on the upper surface of the first ceramic substrate 06 via a metal wire in a wire bonding manner. The pins 3 are welded to the conductive path 0A, thereby achieving an electrical connection of the laser 05 and the pins 03 welded onto the conductive path 0A.
The existing manufacturing process of a laser transmitter cannot achieve wire bonding in opposite directions, that is, cannot achieve establishing an electrical connection on opposite surfaces of a ceramic substrate both in a wire bonding manner. However, the pins 03 are welded to opposite surfaces of the first ceramic substrate 06, so that if an electrical connection to a conductive path on a surface is established in a wire bonding manner, an electrical connection to a conductive path on another surface cannot be established in a wire bonding manner. For such a problem, a second ceramic substrate 07 is added. Referring to FIG. 2, FIG. 3 and FIG. 4, the second ceramic substrate 07 includes a conductive path 0C on an upper surface thereof. A surface where the conductive path 0B is located is laminated onto a surface where the conductive path 0C is located, so as to achieve abutting of the conductive path 0B and the conductive path 0C. Then, the conductive layer is located at a same horizontal plane with the surface where the conductive path 0C on the second ceramic substrate 07 is located. A metal wire is connected to the conductive path 0C of the second ceramic substrate 07 in a wire bonding manner. Through transferring by abutted conductive paths, the laser 05 is electrically connected to the pins 03 welded on the conductive path 0B.
However, due to a narrow conductive path and limited manufacturing process, as shown in FIG. 5, this transferred connection method may causes the conductive paths 0B and 0C to be displaced during abutting, so that a relatively great error exists and consequently causes damage to impedance matching that is preset for high-frequency signals. Impedance matching is a part of microwave electronics, and is mainly used in transmission lines, so as to achieve an objective that all high-frequency microwave signals can be transmitted to a load point, without any signal reflected back to an original point, thereby improving quality of high-frequency signals. High-rate signal transmission requires that a laser transmitter shall meet requirements for impedance matching demanded by high-frequency signals.